Hydrocarbon polymers, particularly ethylene-alpha olefin copolymers, are in widespread use as viscosity index (V.I.) improving additives for oil compositions, particularly lubricating oil compositions. A substantial body of prior art exists directed towards further reacting these ethylene-alpha olefin copolymer V.I. improvers to form a multi-functional V.I. improver. This multi-functional V.I. Improver additive is used to improve not only the V.I. properties of the oil but often to also impart dispersancy so as to suspend soot or sludge that may form during the operation or use of the lubricant in engines. Other multi-functional V.I. improvers have also been reported to impart antiwear and antioxidant properties, both of which are very useful for sustained engine operation.
The most common method to preparing dispersant V.I. improvers involves first grafting ethylene-alpha olefin copolymers with an ethylenically unsaturated component, typically maleic anhydride, followed by reaction of the grafted polymer with a polyamine. The polyamine used to impart the multifunctional characteristics can be highly variable in nature and includes the use of polyamines that are both aliphatic and aromatic in nature.
Many patents disclose the use of alkylene polyamines with grafted copolymers. U.S. Pat. No. 3,316,177, issued Apr. 25, 1967 to Dorer, teaches the use of alkylene polyamines with ethylene-propylene copolymers grafted with maleic anhydride. This composition is taught to be a useful additive for fuels, lubricants and petroleum fractions to inhibit the formation of harmful deposits.
U.S. Pat. No. 4,160,739, issued Jul. 10, 1979, to Stambaugh et al. discloses graft copolymers wherein the backbone polymer is a polymeric hydrocarbon such as substantially linear ethylene-propylene copolymer and the grafted units are the residues of a monomer system comprising maleic acid or anhydride and one or more other monomers copolymerizable therewith. The graft copolymer system is post-reacted with a polyamine compound comprising a primary or secondary amine. The graft copolymers are stated to impart combined, detergent, viscosity index improvement and other useful properties to lubricating oils and hydrocarbon motor fuels.
U.S. Pat. No. 4,735,736, issued Apr. 5, 1988, to Chung discloses oil-soluble ethylene-alpha olefin hydrocarbon polymers, useful as V.I. improvers, preferably ethylene-propylene copolymer, grafted with an unsaturated acid material, such as maleic anhydride, followed by reaction with a polyamine, preferably a tertiary-primary amine, and treatment and/or reaction with aliphatic monoamine. The resulting material is used in oil compositions, such as lubricating oil, as a viscosity index improver having sludge dispersancy properties. The monoamine treatment is stated to inhibit viscosity growth of the additive upon storage.
Polyamines containing aromatic functionality are also well described in the patent literature. U.S. Pat. No. 4,863,623, issued Sep. 5, 1989, to Nalesnik discloses an additive composition comprising a graft and an amine-derivatized copolymer prepared from ethylene and at least one C3 to C10 alpha-monoolefin which has been reacted with at least one olefinic carboxylic acid acylating agent to form one or more acylating reaction intermediates characterized by having a carboxylic acid acylating group within their structure and reacting the reaction intermediate with an amino-aromatic polyamine to form the graft and amine-derivatized copolymer. A lubricating oil composition containing the amine-derivatized copolymer is also disclosed.
U.S. Pat. No. 5,429,757, issued Jul. 4, 1995, and U.S. Pat. No. 5,563,118, issued Oct. 8, 1996, to Mishra et al. disclose an additive composition comprising a graft and derivatized copolymer prepared from an ethylene-alpha-olefin copolymer which has been reacted with at least one olefinic carboxylic acid acylating agent to form one or more acylating reaction intermediates and reacting the reaction intermediate with an amino-aromatic compound. A lubricating oil composition containing the same is also provided.
U.S. Pat. No. 5,942,471, issued Aug. 24, 1999 to Kapuscinski et al., discloses the preparation of dispersant olefin copolymers that also have antioxidant properties. This example uses specific aromatic polyamines such as phenothiazines and N-phenyl-p-phenylenediamine that are reacted in combination with ethylene-propylene copolymers that have been grafted with an ethylenically unsaturated group. The additive composition is said to impart V.I. improver, dispersancy, antiwear, and antioxidant properties when used in a lubricating oil.
The use of monoamines with copolymers grafted with ethylenically unsaturated groups is also described, though to a lesser extent than polyamine functionality. U.S. Pat. No. 7,790,661 B2, issued Sep. 7, 2010 to Covitch et al., teaches the use of several aromatic monoamines to prepare functionalized polymers with improved soot handling performance when used in a lubricating oil.